ASR question in elevated composite deck

[tw]

This building has a 6.5" composite concrete deck (3500 psi, fiber-reinforced, 520 lb cement) that is the second floor of a 3 story building. There is no ground floor so below this deck is not conditioned space. It is covered by metal framing so it is protected from rain.

There was a problem with the terrazzo in first go round, now they want to put a Key EpoCoat epoxy resin to bond terrazzo to slab. Report done by a concrete testing company warns owner to get an ASR expert to comment on the possibility of ASR developing since top of slab will have limited vapor transmission.

Is it possible to pull enough moisture from unconditioned air through metal deck to concrete to get ASR in this case? I have never heard of anything like that.

 

[Ron]

If ASR potential is there, the topping makes no difference...damage will result.

I would not recommend trying to re-bond or coat a delaminated terrazzo surface. Grind or blast it off and start over.

If you are in an area of known aggregate reactivity, the ready-mix supplier should know that and accommodate same in the mix design. Water is not crucial for ASR....alkali quantity is....and it only takes the amount of water in the concrete at the time of mixing and the saturated surface dry condition of the aggregate to help the reaction along.

 

[tw]

This article:

http://nebrconcagg.com/assets/PromotionPages/Mix Design/ASR1.PDF

says (on page 2):

Sufficient moisture.
Moisture allows migration of alkali ions to reaction sites and the resulting gel absorbs moisture, leading to expansion. For this reason, deleterious ASR does not occur in concretes that are dry in service.

 

[Ron]

Good article. Please note that the "magic" number referenced in the article is for the concrete to have a relative humidity of less than 80% internally. It is very common for concrete to have an internal relative humidity of 75 to 80% or even higher...certainly for a time period sufficient to cause ASR.

I've seen ASR continuing in slabs that were over 5 years old and those slabs were inside conditioned space (a shopping center), so the service condition was "dry"; however, ASR still occurred.

As I stated before, there is sufficient water in a normal concrete mix to precipitate ASR even in "dry" service.

 

[tw]

Would you say, all things being equal in this elevated slab, that the slab's ASR potential is the same whether or not they put on the epoxy coating?